This application pertains to the art of solenoid actuated flow control valve assemblies and more particularly to fail-safe flow control valves. The invention is particularly applicable to valves for electrical appliances, especially diswashers, and will be described with particular reference thereto. It will be appreciated, however, that the invention has broader applications in which a fail-safe shut-off of fluid flow is advantageous, such as washing machines, gas appliances, humidifiers, or the like.
Heretofore, flow control valve assemblies for dishwashers and the like have commonly included a valve housing with an inlet port at one end and an outlet port at the other. A first solenoid actuated flow control valving means and a second solenoid actuated flow control valving means were connected hydraulically in series between the inlet and outlet ports. In order for fluids to flow from the inlet port to the outlet port, both flow control valving means had to assume a flow permitting state. If either flow control valving means failed to function, the other was still able to terminate the fluid flow. The solenoid coil of the first valving means and the solenoid coil of the second valving means were electrically connected in parallel to be actuated simultaneously with an actuating voltage applied by a control means.
An exemplary prior art flow control valve assembly is illustrated in U.S. Pat. No. 3,593,957 to Paul Dolter, William McCarty, Jr. and Wesley Swanson, issued July 1971 and assigned to the assignee herein. In this prior art valve assembly, the first and second solenoid coils were designed to minimize the heat generated in the solenoid coils. Because heat varies with the square of the coil current and the coil current varies directly with the actuating voltage and inversely with the coil resistance, the solenoid coils were designed to have a relatively high resistance. Specifically, the solenoid coils were made with a relatively long length of relatively thin, i.e., high gauge, wire which has a relatively high resistance per unit length. In a commercial product manufactured under the Dolter et al. patent, the coil was 6300 turns of #39 copper wire which has a resistance of 0.8466 ohms per foot.
One of the problems with the prior art is that thin, high gauge wire is relatively expensive, because its manufacture is labor intensive. This labor intensity results in thin, high gauge wire being priced significantly higher per pound than thicker, lower gauge wire. However, if a cheaper, lower gauge wire were substituted for the #39 wire, above, the coil current would inrease as would the heat generated.
In this prior art valve assembly, the first and second solenoid valves were connected in parallel. Although they could be connected with the opposite magnetic polarity, they were conventionally connected with the same magnetic polarity such that the magnetic flux of each solenoid flowed in a generally C-shaped path from one of its poles to the other around the exterior of the valve.
Another problem with the prior art resides in placing two coils with the same magnetic pole orientation in close proximity. The repulsion between like magnetic poles causes an interaction between the flux lines of the two coils.
In the prior art, the first and second solenoid coils were each connected with a pair of electrical connection lugs or posts. The actuating voltage was supplied to the solenoid coils by a pair of electrical leads from the dishwasher control circuit and a wiring harness. The wiring harness included a pair of jumper wires for interconnecting the lugs of the first and second solenoid coils together in a parallel circuit connection. Friction connectors were used to connect the electrical control leads and the wiring harness with the solenoid lugs. Because the control leads and the jumper wires both needed to be connected to the same pair of lugs, two dual wire friction connectors were required and two single wire friction connectors at the other ends of the jumper wires were required.
Another problem resides in the prior art wiring connection system including the cost of both labor and materials. The dual wire friction connectors are more expensive than single wire connectors and two jumper wires are more expensive than one.
The present invention contemplates a new and improved solenoid actuated flow control valve assembly for dishwashers and other appliances which overcomes or improves upon the above-referenced problems and others. Yet, it provides a valve assembly which is simple to install and economical to manufacture.